feat(GRO-1794): add booking funnel analytics events

- New analytics utility (src/lib/analytics.ts) with ANALYTICS_EVENTS constants
  and fireAnalyticsEvent() – thin wrapper over window.dispatchEvent, no-op safe
  Built for Plausible/GTM integration later.

- Public booking wizard (Book.tsx): fires step-transition events at each step
  (service → time → contact → submit) plus booking_confirmed on the dedicated
  confirmation page.

- Portal BookingFlow (Appointments.tsx): fires equivalent events for the
  portal booking flow. booking_confirmed fires via useEffect when the inline
  success state is shown.

- BookingErrorPage: fires booking_error on mount (no PII in payload).

Events include step name and flow type (public/portal) but contain no PII:
no names, emails, phone numbers, or pet names in any payload.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/portal/sections/Appointments.tsx

@@ -1,5 +1,6 @@
 import React, { useState, useEffect } from 'react';
 import { Calendar, Clock, Plus, ChevronRight, ChevronDown, Loader2 } from 'lucide-react';
+import { ANALYTICS_EVENTS, fireAnalyticsEvent } from '../../lib/analytics';
 
 export interface Appointment {
   id: string;
@@ -720,6 +721,11 @@ function BookingFlow({ onClose, sessionId }: BookingFlowProps) {
   const [notes, setNotes] = useState('');
   const [recurring, setRecurring] = useState('');
   const [confirmed, setConfirmed] = useState(false);
+  useEffect(() => {
+    if (confirmed) {
+      fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_CONFIRMED, { step: "confirmed", flow: "portal" });
+    }
+  }, [confirmed]);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
   const [submitting, setSubmitting] = useState(false);
@@ -801,6 +807,7 @@ function BookingFlow({ onClose, sessionId }: BookingFlowProps) {
 
       if (response.ok) {
         setConfirmed(true);
+        fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_STEP_SUBMIT, { step: "submit", flow: "portal" });
         setTimeout(() => {
           window.location.reload();
         }, 1500);
@@ -876,6 +883,7 @@ function BookingFlow({ onClose, sessionId }: BookingFlowProps) {
                         onClick={() => {
                           setSelectedPet(pet);
                           setStep(2);
+                          fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_STEP_SERVICE, { step: "service", flow: "portal" });
                         }}
                         className={`w-full flex items-center gap-3 p-3 rounded-xl border text-left transition-colors ${
                           selectedPet?.id === pet.id
@@ -1034,7 +1042,10 @@ function BookingFlow({ onClose, sessionId }: BookingFlowProps) {
                       Back
                     </button>
                     <button
-                      onClick={() => setStep(4)}
+                      onClick={() => {
+                        setStep(4);
+                        fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_STEP_CONTACT, { step: "groomer", flow: "portal" });
+                      }}
                       className="flex-1 px-4 py-2 bg-blue-600 text-white rounded-lg text-sm font-medium"
                     >
                       Next
@@ -1093,7 +1104,10 @@ function BookingFlow({ onClose, sessionId }: BookingFlowProps) {
                       Back
                     </button>
                     <button
-                      onClick={() => setStep(5)}
+                      onClick={() => {
+                        setStep(5);
+                        fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_STEP_TIME, { step: "time", flow: "portal" });
+                      }}
                       disabled={!selectedDate || !selectedTime}
                       className="flex-1 px-4 py-2 bg-blue-600 text-white rounded-lg text-sm font-medium disabled:opacity-50"
                     >